The immune system responds to foreign pathogens, to tumor cells, to autoimmune disease-inducing processes, to allergens, to grafts, through the recognition of the ‘foreign’ or ‘abnormal’ structures, as antigens. Most of those antigens are proteins, which are synthesized either by cells of the host, or by a pathogen. Such antigens are processed (proteolytically digested) into peptide fragments which come to be presented to the responding lymphocytes of the immune system, in a peptide-presenting structure on the surface of the antigen presenting cell. Those peptide presenting structures are called major histocompatibility complex (MHC) molecules. They obtained that name since they were first recognized as products of polymorphic, allelic genes in the MHC locus, which genes control graft rejection among inbred strains of mice.
Animals have developed such complex methods to present and recognize antigens, in order to discriminate peptides derived from ‘self’ molecules, from peptides derived from ‘nonself’ molecules. This invention concerns matter and methods to exploit this fundamental process at the first step in the immune response. Here are revealed compounds and methods to enhance the charging of selected antigenic peptides into certain MHC molecules for a vaccination of the immune system. Such a vaccination will enhance toxic responses against foreignness of an invading pathogen, or a tumor. Other methods using compounds of the invention, can be applied to reinforce the recognition of self, to control autoimmune diseases, allergies, or graft rejection.
The immune response to a specific antigen is mediated by T lymphocytes which recognize peptide fragments of those antigens in the MHC molecules. Within an antigen presenting cell (APC), peptide fragments of a proteolytically processed antigen become bound into the antigenic peptide binding site of major histocompatibility complex (MHC) molecules. These peptide-MHC complexes are then transported to the cell surface for recognition (of both the foreign peptide and the adjacent surface of the presenting MHC molecule) by T cell receptors on responding T lymphocytes. Those T lymphocytes can have either immunoregulatory functions (to help or suppress an immune response) or effector functions (to clear the pathogen or tumor, for example, through a cytotoxic immune response). The antigen-specific recognition event initiates the immune response cascade which leads to a protective immune response, or in the case of autoimmune processes, a deleterious immune response.
Two classes of MHC molecules function as immune system presenters of antigenic peptides to T cells. MHC class I molecules receive peptides from endogenously synthesized proteins, such as an infectious virus, in the endoplasmic reticulum about the time of synthesis of the MHC class I molecules. The MHC class I-bound antigenic peptides are presented at the cell surface to CD8-positive cytotoxic T lymphocytes, which then become activated and can directly kill the virus-expressing cells. In contrast, MHC class II molecules are synthesized in the endoplasmic reticulum with their antigenic peptide binding sites blocked by the invariant chain protein (Ii). These complexes of MHC class II molecules and Ii protein are transported from the endoplasmic reticulum to a post-Golgi compartment where Ii is released by proteolysis and a specific antigenic peptide becomes bound to the MHC class II molecule (Blum et al., Proc. Natl. Acad. Sci. USA 85: 3975 (1988); Riberdy et al., Nature 360: 474 (1992); Daibata et al., Mol. Immunol. 31: 255 (1994); Xu et al., Mol. Immunol. 31: 723 (1994); Xu et al., Antigen Processing and Presentation, Academic Press, NY p227 (1994); Kropshofer et al., Science 270: 1357 (1995); and Urban et al., J. Exp. Med. 180: 751 (1994)).
R. Humphreys (1996) U.S. Pat. No. 5,559,028, and Humphreys et al. (1999) U.S. Pat. No. 5,919,639 revealed the mechanisms by which Ii protein is cleaved, releasing fragments in the course of cleavage to regulate the binding and locking in of antigenic peptides within the antigenic peptide binding site of MHC class II molecules (Adams et al., Eur. J. Immunol. 25: 1693 (1995); Adams et al., Arzneim. Forsch./Drug Research 47: 1069 (1997); and Xu et al., Arzneim. Forsch./Drug Research in press (1999)). One segment of the Ii protein, Ii(77-92), was found to act at an allosteric site outside the antigenic peptide binding site near the end of that site holding the N-terminus of the antigenic peptide. The referenced patents, furthermore, disclosed novel therapeutic compounds and methods to control this initial regulatory, antigenic peptide recognizing event of the immune response by three classes of mechanisms. In the first mechanism, antigenic peptides are spilled from cell surface MHC class II molecules by the action of compounds of the invention.
In the second, the charging of the antigenic peptide binding site on those molecules is promoted with compounds of the invention for binding of other, synthetic peptides. Such inserted peptide sequences can be either antigenic epitopes or nonantigenic peptide sequences which nevertheless bind tightly to block the antigenic peptide binding site. The third mechanism involves altering the rates of association/dissociation of antigenic peptides from those complexes and the nature of the interaction of components of the trimolecular MHC molecule/antigenic peptide/T cell receptor complex, and furthermore the interaction of that trimolecular complex with auxiliary cell-to-cell interaction molecules, in a manner to regulate differentiation and function of the responding T lymphocytes.
The present invention reveals the surprising finding that covalent coupling of the Ii-Key peptide homologs with an antigenic peptide leads to a considerable increase in potency of the presentation of the antigenic epitope. Furthermore, the linker between core, biologically active segment of the Ii-Key peptide need not be a particular peptide sequence derived from the Ii protein. Flexible, simple linkers composed, for example, of repeating methylene (—CH2—) groups, are sufficient and preferred.
The compounds and methods of the present invention can be applied as novel therapeutic and diagnostic compounds in various diseases and conditions. By acting at the initial regulatory, antigenic peptide recognizing event of the immune response, these compounds are favored over other therapeutics with various toxic side effects.
Herein, are revealed utilities in 1) the identification of antigenic epitopes of infectious, malignant, autoimmune and allergic diseases and graft rejection, 2) the use of such epitopes for diagnostic purposes, and 3) the use of such epitopes for therapeutic purposes.